91Ó°ÊÓ

(a) Draw the structure of the transition state for the second propagation step in the chlorination of methane.

Show whether the transition state is product-like or reactant-like and which of the two partial bonds is stronger.

(b) Repeat for the second propagation step in the bromination of methane.

Peroxides are often added to free-radical reactions as initiators because the oxygen-oxygen bond cleaves homolytically rather easily. For example, the bond-dissociation enthalpy of O-Obond in hydrogen peroxide (H-O-O-H)is only 213 kJ/mol (51 kcal/mol). Give a mechanism for the hydrogen peroxide- initiated reaction of cyclopentane with chlorine. The BDE for HO-Clis 210 kJ/mol (50kcal/mol).

When dichloromethane is treated with strong NaOH , an intermediate is generated that reacts like a carbene. Draw the structure of this reactive intermediate, and propose a mechanism for its formation.

The following reaction has a value of${\mathbf{\text{Δ³Ò}}}^{\mathbf{\text{0}}}\mathbf{\text{= -2.1 k´³/³¾´Ç±ô â¶Ä‰(-0.50 â¶Ä‰k³¦²¹±ô/³¾´Ç±ô)}}$

${\mathbf{\text{CH}}}_{\mathbf{\text{3}}}{\mathbf{\text{µþ°ù â¶Ä‰+ â¶Ä‰H}}}_{\mathbf{\text{2}}}\mathbf{\text{³§â€‰â¶Ä‰}}\mathbf{⇄}{\mathbf{\text{ â¶Ä‰C±á}}}_{\mathbf{\text{3}}}\mathbf{\text{³§±á â¶Ä‰+ â¶Ä‰Hµþ°ù}}$

(a) Calculate ${\mathit{K}}_{\mathbf{e}\mathbf{q}}$at room temperature${\mathbf{\text{(25}}}^{\mathbf{\text{0}}}\mathbf{\text{C)}}$ for this reaction as written.

(b)Starting with a$\mathbf{\text{1M}}$ solution of ${\mathbf{\text{CH}}}_{\mathbf{\text{3}}}\mathbf{\text{Br}}$and ${\mathbf{\text{H}}}_{\mathbf{\text{2}}}\mathbf{\text{S}}$, calculate the final concentrations of all four species at equilibrium.

Question: Under base-catalyzed conditions, two molecules of acetone can condense to form diacetone alcohol. At room temperature${25}^{0}c$, aboutof 5%the acetone is converted to diacetone alcohol. Determine the value of$∆G^0$for this reaction.

Question: When ethene is mixed with hydrogen in the presence of a platinum catalyst, hydrogen adds across the double bond to form ethane. At room temperature, the reaction goes to completion. Predict the signs $∆H^{0}and∆S^0$for this reaction. Explain these signs in terms of bonding and freedom of motion.

Question: For each reaction, estimate whether $∆S^0$for the reaction is positive, negative or impossible to predict.

a.

b.The formation of diacetone alcohol:

c.

Question: (a) Propose a mechanism for the free-radical chlorination of ethane.

(b) Calculatefor each step in this reaction

(c) Calculate the overall value offor this reaction.